docs: def estimate_size(self):
          """
          Estimate how many bytes this transaction will be by countng inputs
          and outputs.
          Formula taken from: http://bitcoin.stackexchange.com/a/3011/18150
          """
          # if there are no outs use 1 (because the change will be an out)
          outs = len(self.outs) or 1
          return outs * 34 + 148 * len(self.ins) + 10